Experience and expertise are important on all construction projects, especially when safely and successfully pushing the limits of an emerging technology. Michels Corporation combined the two by using the Direct Pipe methodology to complete a 4,038-foot installation of a 48-inch natural gas pipe in Freemont, TX last August. The project is a North American record for Direct Pipe.
Completing any Direct Pipe installation stretching over ¾-mile is a significant accomplishment. Further challenges posed by this project made it exceptional one.
The Dow Barge Canal crossing was initially designed as a horizontal directional drill (HDD) of a 16-inch pipeline, but an alternate method was sought to better meet the specific environmental and technical requirements of the U.S. Army Corps of Engineers (USACE) for this particular location. In addition to crossing under the canal, the proposed alignment passed under several roads, a rail track and a flood control levee, which was of particular concern to the USACE. Michels reviewed the project and suggested using Direct Pipe and a 48-inch casing pipe to significantly lower the risk of inadvertent release of drilling fluid and hydraulic fracturing, which was the USACE’s primary concern.
Michels had completed a record-length HDD as well as two other Direct Pipe installations on Phillips 66’s Sweeny Midstream Pipeline and signed on for the mammoth third one. Direct Pipe combines elements of tunneling and HDD. On this project, Michels used a Herrenknecht 750-ton pipe thruster to push the pipe into place. A tunnel-boring machine attached to the head of the pipe guides it along the alignment. The spoils and drilling fluids are removed through supply lines inside the product pipe. A separation plant removes spoils from the drilling fluid, allowing it to be recycled.
Length was just one of several elements that made the Dow Barge Canal a unique and challenging project. The largest issue posed by record-length projects is the lack of prior similar projects on which to base plans. However, experienced contractors can overcome that by using information from previous projects. For this Direct Pipe project, the leadership team used data from those projects as a basis for calculations. Additionally, Michels’ significant resources ensured the availability of equipment powerful enough to propel the enormous pipe string even as Michels was simultaneously completing another large Direct Pipe installation in Canada.
Safety is always the top concern. Before any work is started, plans are developed to mitigate risks to the crew, project partners, community and environment. As always, the Direct Pipe crew was briefed on project details and trained to safely negotiate specific challenges that could arise. For this project, that training included working safely in confined spaces and contending with Texas’ oppressive summer heat.
The Dow Barge Canal installation was a critical path and last piece that needed to be completed on the pipeline. As such, the timeline for completion was tight. Michels had about three months to complete the project. To meet that deadline, they mobilized appropriate personnel to work around the clock. They were able to mitigate time-consuming delays by assembling an adequate onsite cache of supplies and equipment to make necessary modifications and repairs.
Site Set Up
The pipe thruster was set up and mining operations were conducted on a relatively small site on property owned by Dow Chemical Co. Due to site limitations, the pipe was strung in two sections requiring a tie-weld during installation. Underground utility congestion posed more obstacles. Michels complied with rules of USACE, Phillips 66, Dow Chemical, and each of the numerous foreign utilities in the ground. It also became necessary to revamp plans for anchoring the pipe thruster to avoid interference with one utility; another required the alignment to take a course that included two compound curves which is very unusual in the Direct Pipe industry.
Because the project was originally designed as an HDD, that profile had already been approved and permitted. To comply with the timeline, Michels adhered to that profile rather than encounter substantial delays caused by redesigning and re-permitting it. As a result, the path was considerably deeper than a typical Direct Pipe alignment. The crossing consisted of an entry angle of 6 degrees vertically and an exit of 10 degrees vertically. The compound curves closely followed the entry and exit angles. They relied on the operators’ finesse, a combination of the manufacturer’s monitoring system, and a series of redundant checks to ensure accurate navigation.
The geology in the area can be a challenging formation for any methodology, including Direct Pipe. After initially mining through silty sand, the bulk of the excavation involved marine clay. To deal with the soil conditions a sophisticated drilling fluid management plan was developed. Proper drilling fluid management was critical to contend with the challenging soils in the pre-determined elevation and to allow for the cutter head’s efficient operation. The drilling fluid was constantly monitored and adjusted for optimal performance.
Authors: Jeff S. Mueller is Operations Manager of Michels Directional Crossings. Patrick O’Donoghue is Trenchless Crossings Manager and Matt Smith is Direct Pipe Manager.